1. Field of the Invention
The invention relates to a helical-scan magnetic-tape apparatus comprising at least three tape guides having axes and including a magnetic-head unit, at least two of said tape guides also acting as tape-threading elements which are movable between a first position, corresponding to a non-operational situation in which the magnetic tape is not in contact with the tape guides, and a second position, corresponding to an operational situation in which the magnetic tape is in contact with the tape guides, which apparatus is constructed to co-operate with a magnetic tape which is wound on two co-planar reels, which each have an axis, and extends between a first and a second reel in the operational situation, a first branch being provided between the first reel and the magnetic-head unit and a second branch being provided between the second reel and the magnetic-head unit, each branch including at least one tape guide, a first path section being provided between said first reel and the tape guide nearest said reel, viewed in the direction of tape transport, a second path section being provided between said second reel and the nearest tape guide, viewed in the direction of tape transport, and further path sections being provided between two tape guides situated one after the other viewed in the direction of tape transport, both the first and the second path section being disposed in the same plane as the reels.
2. Description of the Related Art
A magnetic-tape apparatus of the type referred to above is known from DE 35 09 176 A1. In this known apparatus one branch of the tape-transport path between one reel and the magnetic-head unit is situated at the level of the reel surface and another branch of the tape-transport path between the other reel and the magnetic-head unit is situated partly at reel-surface level and is partly spaced from this level owing to the helical path of the tape around the magnetic-head unit. The latter branch is directed to reel-surface level by means of an inclined pin. For a given position and location of the magnetic-head unit and of the reels the location of this pin cannot be selected freely but must be situated on the line where the plane of the reel surface intersects the plane perpendicular to the tape section which is spaced from the plane of the reel surface. This slightly restricts the constructional freedom and necessitates the use of an additional element, in the present case an inclined pin, in the tape path, exclusively to provide a correction of the tape-transport path with respect to the deviation arising as a result of the helical path of the tape around the magnetic-head unit.
Another important aspect in magnetic-tape apparatuses is that at the location of the magnetic-head unit the tape path is susceptible to the effect of positional tolerances of the tape-path elements. This is in particular so in digital recording, where the tracks to be recorded on and to be read from the tape have a width which is being reduced continually in view of the large amount of information and the consequent requirement of increasing the information density on the tape in order to arrive at a required minimum playing time of a tape. This susceptibility to tolerances depends inter alia on the influence of the positional accuracy of the pin which is inclined relative to the longitudinal direction of the tape and which has a large tape wrapping angle, this influence on the tape path being already substantial in the case of a small deviation.